Zoom optical system and image pickup apparatus provided with the same

ABSTRACT

An zoom optical system comprises a prism component which comprises in order from an object side, an entrance surface having negative refracting power, and a reflecting surface, and movable groups which are movable when either of zooming or focusing is carried out. An image pickup apparatus is provided with the zoom optical system. Thereby, thinning of the image pickup apparatus can be attained sufficiently, and it is possible to shorten the full length of the optical system furthermore, while keeping a moderate zooming ratio.

This application is a divisional application of U.S. patent applicationSer. No. 11/524,788 filed on Sep. 20, 2006 now U.S. Pat. No. 7,679,834,which claims priority to Japanese Application No. 2005-273951 filed onSep. 2, 2005, each of which is expressly incorporated herein in itsentirety by reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light path bending zoom opticalsystem, especially, a zoom optical system and an image pickup apparatusprovided with the same in which a light path bending prism is arrangedin order to realize thinning of depth directions of a digital camera, apersonal digital assistant (PDA), etc.

2. Description of the Related Art

In an image forming optical system which is built in and used for aminiature camera, a personal digital assistant, a cellular phone, etc.,using an electronic image pickup element, such as CCD, C-MOS, etc.,miniaturization, especially thinning of its shape has been stronglydemanded. Furthermore, a zoom optical system with a high image formingperformance which makes an angle of view variable by changing a focallength of image forming optical system is also demanded. To such ademand, many light path bending zoom optical systems in which a prism isarranged at an object side have been proposed and produced commercially.As for such light path bending zoom optical systems, in order to securean angle of view at a wide angle side, to improve an image formingperformance and to make a prism compact, in many cases, one or morenegative lenses are arranged at an object side of the prism. On theother hand, as a zoom optical system without requiring such arrangementof the negative lens, for example, zoom optical systems have beenproposed. Such systems have been disclosed in Publication of theJapanese unexamined patent application, Toku Kai No. 2003-43354,Publication of the Japanese unexamined patent application, Toku Kai. No.2003-107356, Publication of the Japanese unexamined patent application,Toku Kai No. 2004-151552, and Publication of the Japanese unexaminedpatent application, Toku Kai No. 2004-264585.

In these conventional zoom optical systems, an optical system having azoom ratio with about 3 times has been realized by constituting anentrance surface with concave shape, without arranging a lens element atthe object side of a prism. In particular, in zoom optical systems shownin Publication of the Japanese unexamined patent application, Toku KaiNo. 2003-43354 and [Publication of the Japanese unexamined patentapplication, Toku Kai No. 2003-107356, the exit surface of a prism areformed also to be concave surface. A full length of these zoom opticalsystems is about from 7 to 9 times of a diagonal length of an imagepickup screen.

SUMMARY OF THE INVENTION

An zoom optical system according to the present invention comprises, inorder from the object side, a prism component which has an entrancesurface and a reflecting surface having negative refracting power, andan exit surface having positive refracting power and a group havingpositive refracting power, wherein the prism component is arranged atthe utmost object side in optical elements having refracting power inthe zoom optical system, and the lens group comprises two or more movingoptical units which move when at least either zooming or focusing iscarried out.

An zoom optical system according to the present invention comprises, inorder from an object side, a first group having negative refractingpower, and a second group having positive refracting power, a thirdgroup having negative refracting power, and a fourth group havingpositive refracting power. The first group further comprises a prismcomponent which is arranged at the utmost object side, and comprises anentrance surface having a concave surface directed toward the objectside, a reflecting surface, and an exit surface. The second groupfurther comprises an aperture stop. In such constitution, when zoomingis carried out from a wide angle end to a telephoto end, the secondgroup and the third group move toward the object side, respectively, andan interval between the first group and the second group decreases, andan interval between the second group and the third group, and aninterval between the third group and the fourth group increaserespectively, and the following conditions (1) and (2) are satisfied.1.4<G23W/G34W<3  (1)0.4<G23T/G34T<1.5  (2)where G23W is an interval between the second group and the third groupat a wide angle end, G34W is an interval between the third group and thefourth group at a wide angle end, G23T is an interval between the secondgroup and the third group at a telephoto end, and G34T is an intervalbetween the third group and the fourth group at a telephoto end.

A zoom optical system according to the present invention comprises, inorder from an object side, a first group having negative refractingpower, and a second group having positive refracting power, a thirdgroup having negative refracting power, and a fourth group havingpositive refracting power, wherein the first group comprises a prismcomponent arranged at the utmost object side, which comprises anentrance surface, a reflective surface, and an exit surface, concavesurface of which is directed toward to the object side. The second groupfurther comprises an aperture stop, wherein when zooming is carried outfrom a wide angle end to a telephoto end, the second group and the thirdgroup move to the object side, respectively, and an interval between thefirst group and the second group decreases, and an interval between thesecond lens group and the third group, and an interval between the thirdgroup and the fourth group becomes large, respectively. When focusing iscarried out, an interval between the second group and the third groupchanges. When focusing which is carried out from the infinite distancetoward a very near position is based, as for a rate of the amount ofmovement of the second group and the third group, the second groupbecomes main at the wide angle side, and the third group becomes main atthe telephoto side.

A zoom optical system according to the present invention comprises inorder from an object side, a first group having negative refractingpower, and a second group having positive refracting power, a thirdgroup having negative refracting power, and group with positiverefracting power, wherein the first group comprises a prism componentarranged at the utmost object side, which comprises an entrance surface,a reflective surface, and an exit surface, concave surface of which isdirected toward to the object side, and furthers, and the second groupcomprising an aperture stop, wherein when zooming is carried out from awide angle end to a telephoto end. The second group and the third groupmove to the object side, respectively, and an interval of the firstgroup and the second group decreases, and an interval of the secondgroup and the third group decreases, and an interval of the third groupand the fourth group becomes large respectively, and further comprises alight quantity adjustment part arranged between a lens surface arrangedat the utmost image side in the second group and a lens surface arrangedat the utmost object side in the third group

An image pickup apparatus according to the present invention comprises azoom optical system and an image pickup element, wherein the zoomoptical system comprises a first group having a prism component which isarranged at the utmost object side among the zoom optical system and hasan entrance surface and a reflective surface, a concave surface of whichis directed toward the object side, at least two moving optical unitswhich are arranged at an image side from the first group and movablewhen zooming is carried out, a last group which is arranged at theutmost image side in the zoom optical system at the image side and haspositive refracting power, and an aperture stop arranged between thefirst group and the last group, wherein when zooming carried out from awide angle end to a telephoto end, an entrance pupil formed by theaperture stop is moved toward the object side, and an exit pupil formedby the aperture stop in the optical system arranged nearer to the objectside than the last group is moved toward the object side, and the lastgroup comprises a lens component having a surface at an object sidewhich is the first aspherical surface a, and a surface at an image sidewhich is the second aspherical surface b, which has a convex surfacedirected toward the image side near the optical axis, and a point ofinflection at a cross-section including the optical axis, and eachaspherical surface satisfies the following conditions (3) to (5).0.08<(ha11−ha07)/I<0.3  (3)−0.1<ha07/I<0.07  (4)0.45<Cb/I<1  (5)where with respect to the aspherical surface a, ha07 is a distance froma reference plane to the aspherical surface a of the direction of anoptical axis in 35% of height of an effective diagonal length of animage pickup element (here said reference plane has a vertex of theaspherical surface a and is perpendicular to the optical axis, and, adirection from the object side toward the image side is set to be apositive direction), and, ha11 is a distance from the reference plane tothe aspherical surface a of the direction of an optical axis in 55% ofheight of the effective diagonal length of an image pickup element (herethe reference plane has a vertex of the aspherical surface a and isperpendicular to the optical axis, and, the direction from the objectside to the image side is set to be a positive direction), I is 50% oflength of the effective diagonal length of the image pickup element, andCb is a height from the optical axis to the point of inflection of theaspherical surface b. Here, the effective diagonal length is diagonallength of the greatest domain (effective image pickup surface) which isused for recording, displaying, and printing of an image, on the lightreceiving surface of an image pickup element.

An mage pickup apparatus according to the present invention comprises azoom optical system and an image pickup element, wherein the zoomoptical system comprises a prism component having an entrance surfacewhich is arranged at the utmost object side in elements havingrefracting power in the optical system, a concave surface of which isdirected toward the object side, a reflecting surface, and an exitsurface, and at least one moving optical unit which has refracting powerand is moved, and further, the following conditions (6) to (8) aresatisfied.4<rp1/I<−1.8  (6)8<L/I<12  (7)2.5<M/I<7  (8)where rp1 is a radius of curvature of the entrance surface of a prismcomponent, L is an optical path length of a zoom optical system, I is50% of length of the effective diagonal length of an image pickupelement, and M is total of the amount of movement of each group at awide angle region and at a telephoto region, and the focal length of thetelephoto region is 2.3 time or more and 5 times or less of the focallength at the wide angle region.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of the preferredembodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are developed views of light path along an opticalaxis showing an optical arrangement of a zoom optical system at a wideangle end, a middle position and a telephoto end when photographingdistance is infinite, respectively, of the embodiment 1 according to thepresent invention.

FIGS. 2A-2E, 2F-2J, and 2K-2O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height,and showing the aberrations at a wide angle end, a middle angle positionand a telephoto end when a photographing distance is infinite,respectively, of a zoom optical system of the embodiment 1 according tothe present invention.

FIGS. 3A-3E, 3F-3J, and 3K-3O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height,and showing the aberrations at a wide angle end, a middle position and atelephoto end, respectively, when each photographing distance is 300 mmas very close distance.

FIGS. 4A, 4B and 4C are developed views of light path along an opticalaxis showing an optical arrangement of a zoom optical system of theembodiment 2 according to the present invention, and showing states at awide angle end, a middle position and a telephoto end when aphotographing distance is infinite, respectively.

FIGS. 5A-5E, 5F-5J, and 5K-5O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height ofa zoom optical system in the embodiment 2 according to the presentinvention, and showing the aberrations at a wide angle end, a middleposition and a telephoto end when a photographing distance is infinite,respectively.

FIGS. 6A-6E, 6F-6J, and 6K-6O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height ofa zoom optical system in the embodiment 2 according to the presentinvention, and showing the aberrations at a wide angle end, a middleposition and a telephoto end, respectively, when each photographingdistance is 300 mm as very close distance.

FIGS. 7A, 7B and 7C are developed views of light path along an opticalaxis showing an optical arrangement of a zoom optical system of theembodiment 3 according to the present invention, and showing states at awide angle end, a middle position and a telephoto end when aphotographing distance is infinite, respectively.

FIGS. 8A-8E, 8F-8J, and 8K-8O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height ofa zoom optical system in the embodiment 3 according to the presentinvention, and showing the aberrations at a wide angle end, a middleposition and a telephoto end when a photographing distance is infinite,respectively.

FIGS. 9A-9E, 9F-9J, and 9K-9O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height ofthe embodiment 3 according to the present invention, and showing theaberrations at a wide angle end, a middle position and a telephoto end,respectively, when each photographing distance is 300 mm as very closedistance.

FIGS. 10A, 10B and 10C are developed views of light path along anoptical axis showing an optical arrangement of a zoom optical system ofthe embodiment 4 according to the present invention, and showing statesat a wide angle end, a middle angle position and a telephoto end when aphotographing distance is infinite, respectively.

FIGS. 11A-11E, 11F-11J, and 11K-11O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height ofa zoom optical system in the embodiment 4 according to the presentinvention, and showing the aberrations at a wide angle end, a middleangle position and a telephoto end when a photographing distance isinfinite, respectively.

FIGS. 12A-12E, 12F-12J, and 12K-12O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height ofa zoom optical system in the embodiment 4, and showing the aberrationsat a wide angle end, a middle angle position and a telephoto end when aphotographing distance is 300 mm as very close distance, respectively.

FIGS. 13A, 13B and 13C are developed views of light path along anoptical axis showing an optical arrangement of a zoom optical system ofthe embodiment 5 according to the present invention, and showing statesat a wide angle end, a middle angle position and a telephoto end when aphotographing distance is infinite, respectively.

FIGS. 14A-14E, 14F-14J, and 14K-14O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height ofa zoom optical system in the embodiment 5, and showing the aberrationsat a wide angle end, a middle angle position and a telephoto end when aphotographing distance is infinite, respectively.

FIGS. 15A-15E, 15F-15J, and 15K-15O are characteristics diagrams showingspherical aberration, astigmatism, distortion, chromatic aberration ofmagnification, and longitudinal aberration of a specific image height,of a zoom optical system in the embodiment 5, and showing theaberrations at a wide angle end, a middle position and a telephoto end,respectively, when each photographing distance is 300 mm as a very closedistance.

FIG. 16 is a front perspective diagram showing the outside view of anelectronic camera using the optical system of the present invention.

FIG. 17 is a back perspective diagram of the electronic camera of FIG.16.

FIG. 18 is an internal block diagram showing the composition of theelectronic camera of FIG. 16.

FIG. 19 is a block diagram showing a circuit composition for controllingeach part in an embodiment of the electronic camera.

FIG. 20 is a front perspective diagram of the personal computer in whichan optical system of the present invention is incorporated as anobjective optical system, where the cover is opened.

FIG. 21 is a sectional drawing of a photographing optical systemincorporated in the personal computer.

FIG. 22 is a side elevation of FIG. 20.

FIGS. 23A, 23B, and 23C are a front elevation, a side elevation, andsectional drawing of a photographing optical system of a cellular phonewith which an optical system of the present invention is incorporated asan object optical system, respectively.

FIG. 24 is an explanatory diagram about the conditions (3), (4), and(5).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In advance of explanation of embodiments, the more concrete function andeffect of the present invention will be explained.

A zoom optical system of the first invention, comprises in order from anobject side, a prism component which has an entrance surface havingnegative refracting power, a reflecting surface, and an exit surfacehaving positive refracting power, and at least two movable groups whichcan be moved when either zooming or focusing is carried out, wherein thegroups have positive refracting power as a whole.

As shown in the zoom optical system of the first invention, by using theprism component which has an entrance surface having negative refractingpower, and an exit surface having positive refracting power, whilesuppressing the refracting power of the whole prism component frombecoming too strong in a negative direction, an entrance surface havingstrong negative refracting power can be arranged. By this, a size of theentrance surface of the prism component can be made small, an incidentlight height to the prism component can be made low, and accordingly, itenables to contribute achieving of thinning. If it is constituted inthis way, by balancing an amount of generation of a curvature of fieldand a distortion generated on a concave surface which is an entrancesurface of the prism component through a convex surface which is an exitsurface of the prism component, the full length of groups arranged atthe image side nearer than the prism component can be shortened. Thatis, if the balance of the amount of the curvature of field and theamount of distortion generated in the prism component is lost, anaberration-correction surface in a portion where luminous flux accordingto an image height is separated in order to correct both of aberrationsgood, is increased, and consequently, the full length of a zoom opticalsystem has to be lengthened as a result. As for the prism component, itis desirable to have refracting power which is from weak positiverefracting power to negative refracting power, and it is necessary toconstitute so that lens element group at the image side may havepositive refracting power from a wide angle state to a telephoto state.If two movable groups are arranged, by changing the focal length,focusing can be carried out on an image surface.

An zoom optical system according to the second invention comprises, inorder from an object side, a first group having negative refractingpower, and a second group having positive refracting power, a thirdgroup having negative refracting power, and a fourth group havingpositive refracting power, the first group further comprising a prismcomponent which is arranged at the utmost object side, and comprises anentrance surface having a concave surface directed toward the objectside, a reflecting surface, and an exit surface, and the second groupfurther comprising an aperture stop, wherein, when zooming is carriedout from a wide angle end to a telephoto end, the second group and thethird group move toward the object side, respectively, and an intervalbetween the first group and the second group decreases, and an intervalbetween the second group and the third group, and an interval betweenthe third group and the fourth group become wide respectively, and thefollowing conditions (1) and (2) are satisfied.1.4<G23W/G34W<3  (1)0.4<G23T/G34T<1.5  (2)where G23W is an interval between the second group and the third groupat a wide angle end, G34W is an interval between the third group and thefourth group at a wide angle end, G23T is an interval between the secondgroup and the third group at a telephoto end, and G34T is an intervalbetween the third group and the fourth group at a telephoto end,

If a prism component is used for the first group, thinning of an imagepickup optical system constituted by using a zoom optical system can beattained. In this case, if it is constituted so that a concave surfaceof an entrance surface may be directed toward the object side, it ispossible to arrange the prism component at the utmost object side, whileminiaturizing the prism component, compared with the conventionalcomposition in which a negative lens element and the like are arrangedindependently at the object side of the prism component like the zoomoptical system shown in the patent documents 1 to 4, further thinning ofthe image pickup optical system can be achieved.

In the second invention, a prism component means the optical element,wherein with respect to the optical element including a prism, only asurface which is arranged at the utmost object side, and only a surfacewhich is arranged at the utmost image side contacts with air, and no airinterval contains between the surfaces. As for prism component, it isdefined that a prism itself, or a cemented element in which a lens and aprism is cemented is one unit. As for a lens component, it is definedthat, with respect to the lens, only a surface which is arranged at theutmost object side, and only a surface which is arranged at the utmostimage side contacts with air, and no air interval contains between thesurfaces, and single lens or a cemented lens is one unit.

If the second group has a substantial aperture adjusting function, itbecomes easy to miniaturize a prism component, and a diameter after thethird group, and to bring an incident angle of the luminous flux to theimage pickup element close perpendicularly. As a constitution having asubstantial aperture adjusting function, besides a composition in whichan aperture stop is arranged directly in the second group, for example,a substantial aperture stop may be constituted by a part of mirrorholding frame incorporating the lens which constitutes the second group.

When zooming is carried out from a wide angle end to a telephoto end, bymoving the second group and the third group toward the object side,respectively, by making an interval between the first group and thesecond group small, and by extending an interval between the secondgroup and the third group G3, and an interval between the third group G3and the fourth group G4, zooming function can be distributed with twogroups, that is, the second group and the third group. Accordingly,change of an aberration can be suppressed, and it becomes easy to securepermissible conditions on manufacturing such as decentering and thelike.

In particular, in the third group, when zooming is carried out from awide angle end to a telephoto end, by extending an interval to thesecond group, a telephoto type power can be strengthened and theshortening effect of the full length can be obtained. Further, byextending an interval to the fourth group, an incidence height of theluminous flux at circumference to the fourth group can be made high, andit becomes easy to correct well off-axis aberration, especiallydistortion through the fourth group.

In the fourth group, since it has a function to adjust an exit pupilposition, and when zooming is carried out from a wide angle end to atelephoto end, the second group having an aperture stop, and the thirdgroup having a negative component move away toward the object side, bychanging the incident light height of the chief ray to each image height(it is made high at the telephoto end), it becomes easy to correct wellthe off-axis aberration, especially the distortion, irrespective to azooming state. Also, in the entrance surface of the first group, sincethe direction of the off-axis luminous flux at the wide angle end sideenters into a position distant far from the optical axis compared with acase of the telephoto-end side, it becomes easy to correct the off-axisaberration the wide angle end side. Thus, by constituting the firstgroup to the fourth group, it becomes easy to correct aberrations withsufficient balance over the range from the wide angle end to thetelephoto end.

It is not desired that if it is less than the lower limit of condition(1), the third group and the fourth group separate too much at a wideangle end. On the other hand, it is not desired that if it exceeds theupper limit of condition (1), an interval between the second group andthe fourth group becomes large too much. It is not desired that if it isless the lower limit of condition (2), an interval between the secondgroup and the third group becomes small too much, and a telephotoarrangement becomes weak. On the other hand, it is not desired that ifit exceeds the upper limit of condition (2), an interval between thethird group and the fourth group becomes close too much.

An image pickup apparatus according to the third invention comprises azoom optical system and an image pickup element, wherein the zoomoptical system comprises a first group having a prism component which isarranged utmost at an object side among the zoom optical system and hasan entrance surface and a reflecting surface, a concave surface of whichis directed toward the object side, at least two moving optical unitswhich are arranged at an image side from the first group and movablewhen zooming is carried out, a last group which is arranged at theutmost image side in the zoom optical system at the image side and haspositive refracting power, and an aperture stop arranged between thefirst group and the last group, wherein when zooming is carried out froma wide angle end to a telephoto end, an entrance pupil formed by theaperture stop is moved toward the object side, and an exit pupil formedby the aperture stop in the optical system arranged nearer to the objectside than the last group is moved toward the object side, and the lastgroup comprises a lens component having a surface at an object sidewhich is the first aspherical surface a, and a surface at an image sidewhich is the second aspherical surface b. The second aspherical surfaceb has a convex surface directed toward the image side near the opticalaxis, and a point of inflection at a cross-section including the opticalaxis, and each aspherical surface satisfies (5) the following conditions(3) to (5).0.08<(ha11−ha07)/I<0.3  (3)−0.1<ha07/I<0.07  (4)0.45<Cb/I<1  (5)where with respect to the aspherical surface a, ha07 is a distance froma reference plane to the aspherical surface a of the direction of anoptical axis in 35% of height of an effective diagonal length of animage pickup element (here said reference plane has a vertex of theaspherical surface a and is perpendicular to the optical axis, and, adirection from the object side toward the image side is set to be apositive direction), and, ha11 is a distance from the reference plane tothe aspherical surface a of the direction of an optical axis in 55% ofheight of the effective diagonal length of an image pickup element (herethe reference plane has a vertex of the aspherical surface a and isperpendicular to the optical axis, and, the direction from the objectside to the image side is set to be a positive direction), I is 50% oflength of the effective diagonal length of the image pickup element, andCb is a height from the optical axis to the point of inflection of theaspherical surface b. (refer to FIG. 24).

As shown in the second invention, if a prism component is used for thefirst group, thinning of an image pickup optical system constituted byusing a zoom optical system can be attained. Here, if a concave surfaceof the entrance surface is directed toward the object side, a prismcomponent can be arranged at the utmost object side, while it isminiaturized, and further thinning of the image pickup optical systemcan be achieved.

In the fourth group, by using a function to adjust an exit pupilposition, and by changing the incident light height of the chief ray toeach image height (it is made high at the telephoto end) when zooming iscarried out from a wide angle end to a telephoto end, in addition to theeffect of the first group, it becomes easy to correct well the off-axisaberration, especially the distortion, irrespective to a zooming state.Also, in the entrance surface of the first group, since the direction ofthe off-axis luminous flux at the wide angle end side enters into aposition distant far from the optical axis compared with a case of thetelephoto-end side, it becomes easy to correct the off-axis aberrationthe wide angle end side. Thus, by constituting the first group to thefourth group, it becomes easy to correct aberrations with sufficientbalance over the range from the wide angle end to the telephoto end.

On the other hand, different from the case of the third invention, if itis constituted such that an entrance pupil position is moved toward animage side at the telephoto-end side, correction of aberrations becomesdifficult, since in the entrance surface of the first group, due to awide angle of view at the wide-angle-end side, and a distant entrancepupil, there is no difference of incident luminous fluxes to acircumferential image height. (namely, a possibility that the domainwhere paraxial luminous flux and off-axis luminous flux pass an entrancesurface of the first group overlap becomes large)

The conditions (3), (4), and (5), are conditions which specify desirableform of an aspherical surface to demonstrate functions of the fourthgroup. The conditions (3) and (4), show that an aspherical surface a atan object side has weak refracting power in the central part, and It hasacute strong refracting power at a circumference part.

This serves as form advantageous to especially aberration correction ata telephoto end side. If it becomes less than the lower limit ofcondition (3), the curvature of the form of a circumference part becomestight too much, and processing becomes difficult and disadvantageouswith respect to productivity. On the other hand, if it exceeds the upperlimit of condition (3), especially the off-axis aberration of atelephoto side will get worse. If it becomes less than the lower limitof condition (4), the degree of change of the curvature of this surface(aspherical surface a) becomes tight, and it is not desirable. On theother hand, when it exceeds the upper limit of condition (4), if it isattempted to distinguish between the refracting power of the centralpart and the circumference part of the lens surface concerned, the lensform becomes complicated and it is disadvantageous for improving animage forming performance on the whole.

The condition (5) shows that as for the refracting power of theaspherical surface b from the central portion to the circumferenceportion, the divergence function becomes strong. If condition (5) issatisfied, positive refracting power to the luminous flux to thecircumference image height at a telephoto end side will become smallrather than that of a wide-angle-end side, and it becomes advantageousfor suppressing change of a substantial exit pupil position.

By combining with the aspherical surface a at the object side, off-axisaberrations such as circumference image height, chromatic aberration,coma aberration, distortion and the like can be corrected well.

That is, the off-axis aberration at the wide angle end side is mainlycorrected well in the first group, and even if it degrades theaberration at the telephoto end side, it becomes easy to obtain a goodimage forming performance on the whole. If it is less than the lowerlimit of condition (5), the luminous flux at circumference at thetelephoto end side and a lot of luminous flux at circumference at thewide angle end sides are influenced together by lens function at thecircumference side rather than from the point of inflection, andaccordingly it becomes disadvantageous when performances to the luminousflux are distinguished. If it is less than the lower limit of condition(5), the luminous flux at circumference at the telephoto end side and alot of luminous flux at circumference at the wide angle end side receivetogether lens function at the center side rather than from the point ofinflection, and accordingly it becomes disadvantageous when performancesto the luminous flux are distinguished (That is, since a possibilitythat paraxial luminous flux and off-axis luminous flux are overlappedbecomes large, correction of aberrations becomes difficult).

A zoom optical system according to the fourth invention comprise, inorder from an object side, a first group having negative refractingpower, and a second group having positive refracting power, a thirdgroup having negative refracting power, and a fourth group havingpositive refracting power, wherein the first group comprises a prismcomponent arranged at the utmost object side, which comprises anentrance surface, a reflecting surface, and an exit surface, concavesurface of which is directed toward to the object side, and the secondgroup comprising an aperture stop, wherein when zooming is carried outfrom a wide angle end to a telephoto end, the second group of the thirdgroup move to the object side, respectively, and an interval between thefirst group and the second group decreases, and an interval between thesecond lens group and the third group, and an interval between the thirdgroup and the fourth group becomes large, respectively, and whenfocusing is carried out, an interval between the second group and thethird group changes. When focusing which is carried out from theinfinite distance toward a very near position is based, as for a rate ofthe amount of movement of the second group and the third group, thesecond group becomes main at the wide angle side, and the third groupbecomes main at the telephoto side.

In a zoom optical system wherein, with respect to arrangement ofrefracting power, the first group is negative, the second group ispositive, the third group is negative, and the fourth group is positive,and furthermore the second group and the third group are moved at thetime of zooming, taking a state such that an interval between the thirdgroup and the fourth group is brought close at the a wide angle end. Onthe other hand, an interval between the first group and the second groupis brought close at the telephoto end, becomes advantageous conditionsfor the full length shortening and the aberration corrections of theoptical system.

In this case, if it is constituted such that focusing is carried out bythe third group or the fourth group, it is required that the intervalbetween the third group and the fourth group, in order to secure a spacerequired for focusing at the wide angle end also. On the other hand, ifit is constituted such that focusing is carried out by the second group,it is required that the interval between the first group and the secondgroup, in order to secure a space required for focusing at the telephotoend also. However, focusing in the first group is not desirable since itmoves a prism component. Therefore, according to the zoom optical systemof the present invention, in order to solve such the subject and tolessen groups to be driven at the time of zooming, it is constitutedsuch that focusing is carried out the second group and the third group.

When focusing which is carried out toward a very near direction from theinfinite distance is based, it is constituted such that the second groupis made to be main at the wide angle side about the rate of the movementand the third group is made to be main at the telephoto side. Ifconstituted in this way, it becomes easy to bring the interval betweenthe third group and the fourth group close at the wide angle end, andalso it becomes easy to bring the interval between the first group andthe second group close at the telephoto end. As a result, it becomespossible to shorten the full length of the zoom optical system.

A zoom optical system according to the fifth invention comprise, inorder from an object side, a first group having negative refractingpower, and a second group having positive refracting power, a thirdgroup having negative refracting power, and a group with positiverefracting power, wherein the first group comprises a prism componentarranged at the utmost object side, which comprises an entrance surface,a reflecting surface, and an exit surface, concave surface of which isdirected toward to the object side, and furthers, and the second groupcomprising an aperture stop, wherein when zooming is carried out from awide angle end to a telephoto end. The second group and the third groupmove to the object side, respectively, and an interval of the firstgroup and the second group decreases, and an interval of the secondgroup and the third group decreases, and an interval of the third groupand the fourth group becomes large respectively, and further comprises alight quantity adjustment part arranged between a lens surface arrangedat the utmost image side in the second group and a lens surface arrangedat the utmost object side in the third group.

It is required that an interval between the first group and the secondgroup is made close at the telephoto end, and an interval between thethird group and the fourth group is made close at the wide angle end. Asfor the interval of the second group and the third group, it is requiredthat it has a telephotograph nature over the whole zooming range, andaccordingly, it is necessary to secure a certain amount of interval.Although it is desired that the second group has a function ofsubstantial aperture stop. Besides this, it is desirable to arrange acomponent which adjusts a quantity of light, including shading componentbetween the second group and the third group. By this arrangement, anefficient zoom constitution is attained, and miniaturization with goodperformance as a whole can be achieved.

An image pickup apparatus according to the sixth invention comprises azoom optical system and an image pickup element, wherein the zoomoptical system comprises a prism component having an entrance surfacewhich is arranged utmost at an object side, a concave surface of whichis directed toward the object side, a reflecting surface and an exitsurface, and further the following conditions (6) to (8) are satisfied.−4<rp1/I<−1.8  (6)8<L/I<12  (7)2.5<M/I<7  (8)where rp1 is a radius of curvature of the entrance surface of a prismcomponent, L is an optical path length of a zoom optical system, I is50% of length of the effective diagonal length of an image pickupelement, and M is total of the amount of movement of each group at awide angle region and at a telephoto region, and the focal length of thetelephoto region is 2.3 times or more and 5 times or less of the focallength of the wide angle region.

The condition (6) is a condition for attaining miniaturization, whileobtaining a good optical performance, in a constitution such that aprism component which has an entrance surface having a concave surfacedirected toward an object side, a reflecting surface and an exit surfaceis arranged at the utmost object side. If the upper limit of condition(6) is exceeded, an entrance pupil position becomes close at the wideangle end side, and separation of luminous flux worsens by the imageheight at the entrance surface, and accordingly it becomes difficult toget a good off-axis performance. If the lower limit of condition (6) isnot reached, good optical performance is hard to achieve and wouldrequire an additional lens element to be arranged on the object side,which is disadvantageous for miniaturization. Falling below the lowerlimit of condition (7) is not desirable, because the full length becomesso short as to bring about a complicated structure for zooming and forlens group arrangement. On the other hand, exceeding the upper limit ofcondition (7) is not desirable, because, in a situation where zoomconstitution is simplified, fluctuation of an entrance pupil positionbecomes large, or the entrance pupil position at the wide angle endbecomes too distant, and accordingly the prism becomes large. Thecondition (8) is a condition which specifies the balance between thelength of lens constitution and the zoom moving region. If the upperlimit of the condition (8) is exceeded, it is difficult to strike abalance between various aberration corrections. On the other hand, ifthe lower limit of the condition (8) is not reached, in order to securea considerable magnification ratio, each group is required to have astrong refracting power, which would easily generate aberrations. In thezoom optical system according to the seventh invention, in one of thezoom optical system of the first to sixth invention, it is desired thatthe prism component has negative refracting power as a whole. In thisway, by diffusing exit luminous flux, especially correction of sphericalaberration or longitudinal aberration of specific image can be carriedout easily by the lens element group at the image side. In the zoomoptical system according to the eighth invention, in one of the zoomoptical system of the first to seventh invention, it is desired that thefollowing condition (9) is satisfied:−0.55<ΦP·fw<0  (9)where the refracting power of the prism component is ΦP, and the focallength of the zoom optical system at the wide angle end is fw.

If it exceeds the upper limit of condition (9), in the group at theimage side, especially correction of spherical aberration orlongitudinal aberration in a specific image becomes difficult, and itbecomes necessary to increase the number of lenses composed of a groupand to use an expensive material and a lens element with high processingcost in order to obtain a high image forming performance. It is notdesirable for productivity and cost. If it is less than the lower limitof condition (9), a concave surface form on an entrance surface becomesdeep, and the processability of the prism component becomes worse, or itbecomes unable to keep balances among a curvature of field, chromaticaberration, and distortion.

In the zoom optical system according to the ninth invention, in one ofthe zoom optical system of the first to eight invention, it is desirableto satisfy the following condition (10), where paraxial radius ofcurvature of an entrance surface is rP1 and the paraxial radius ofcurvature of the exit surface is rP2 as for the prism component.−1<(rP1−rP2)/(rP1+rP2)<−0.2  (10)

If it exceed the upper limit of condition (10), in the group at theimage side, especially correction of spherical aberration orlongitudinal aberration in a specific image becomes difficult, and itbecomes necessary to increase the number of lenses composed of a groupand use an expensive material and a lens element with high processingcost in order to obtain a high image forming performance. If it is lessthan the lower limit of condition (10), a concave surface form on anentrance surface becomes deep, and the processability of the prismcomponent becomes worse, or it becomes unable to keep balances among acurvature of field, chromatic aberration, and distortion.

In the zoom optical system according to the tenth invention, one of thefirst to ninth invention, it is desired that an entrance surface and anexit surface of the prism component are aspherical surfaces, areflecting surface of the prism component is a flat plane, and each ofaspherical surfaces of the prism component has a shape such thatrefracting power becomes weak as it departs from an optical axis.(namely, a shape in which the absolute value of a local curvaturebecomes small as it departs from the optical axis) If it is constitutedsuch that the reflecting surface has a curvature, or it has anaspherical surface, it becomes advantageous for a paraxial layout sincea surface having refracting power can be arranged near the entrancesurface. However, on the other hand, in order to correct an asymmetricalaberration generated on the reflecting surface having aspherical surfaceform, it is necessary to arrange an asymmetrical surface to an opticalaxis at another surface. As a result, therefore, it becomesdisadvantageous in view of a number of lenses, processing cost, etc. Theaspherical surface forms of the entrance surface and the exit surfaceare formed so that refracting power may become weak as each of themdeparts from the optical axis similarly. By such constitution mentionedabove, meniscus form is maintained, and it becomes easy to control thebalance of an off-axis aberration by using a fact that overlapped stateof the luminous flux of each image height changes at the entrancesurface and the exit surface. Moreover, if the aspherical surfaces ofthe entrance surface and the exit surface are formed to be symmetricalwith respect to the axis, it is desirable for processing or aberrationscorrection.

In the zoom optical system according to the eleventh invention, in oneof the zoom optical system of the first, the third or the sixthinvention 1, it is desired that it comprises in order from an objectside, a first group which comprises the prism component, and hasnegative refracting power group which comprises an aperture stop and haspositive refracting power, a third group having negative refractingpower, and a fourth group having positive refracting power, wherein thesecond group and the third group are the moving optical units, and whenzooming is carried out from a wide angle end to a telephoto end, whilethe second group and the third group are moved to the object siderespectively, an interval between the first group and the second groupdecreases, and an interval between the third group and the fourth groupbecomes large. As shown in the zoom optical system of the firstinvention, by moving the second group and the third group toward theobject side, while extending the interval, respectively, zoomingfunction is distributed to these two groups, and change of an aberrationcan be suppressed, and accordingly, it becomes easy to securepermissible conditions on manufacturing such as decentering and thelike. If it is constituted such that the fourth group has a function toadjust an exit pupil position, and when zooming is carried out from awide angle end to a telephoto end, the second group having an aperturestop, and the third group having a negative component are moved awaytoward the object side, it becomes easy to correct well the off-axisaberration, especially the distortion, irrespective to a zooming state,by changing the incident light height of the chief ray to each imageheight.

In a zoom optical system of the twelfth invention, in one zoom opticalsystem according to one of the first to the fifth and the eleventhinvention, it is desired that the third group comprises one negativelens. It is constituted so that correction of the off-axis aberration ofat the wide angle end side is carried out by the first group, correctionof an on-axis aberration is carried out by the second group, andcorrection of the off-axis aberration at the telephoto end side iscarried out mainly by the fourth group, and furthermore, the third groupconsists of one negative lens so that paraxial functions such as zoomingfunction, function of compensator, etc. are carried out mainly by thethird group. Thus, if the third group is constituted with one negativelens, it becomes advantageous for miniaturization as the full length ofa zoom optical system is shortened.

In the zoom optical system of the thirteenth invention, it is desiredthat the one negative lens constituting the third group is formed byplastic molding since the function of the third group is mainlymagnification in the zoom optical system of the twelfth invention. It isdesired that restrictive conditions with respect to refractive index anddispersion of the material are made loose in order to be advantageous inrespect of cost or weight.

In the zoom optical system according to the fourteenth invention, it isdesired that the first group is constituted such that a negative lensand a positive lens are arranged at the image side of the prismcomponent in one of the zoom optical system of the second to fourthinventions, or the eleventh to thirteenth inventions. It is desirable tomake such arrangement, since the chromatic aberration of magnificationat the wide angle side can be corrected well.

In the zoom optical system of the fifteenth invention, it is desiredthat in a zoom optical system of the fourteenth invention, therefractive index of the negative lens and the positive lens is 1.7 ormore, respectively. If the refractive index is made high and the radiusof curvature is made loose, the full length can be shortened, andaccordingly it can contribute to miniaturization. Especially, if theinterval between the backside principal point of the first group and thesecond group can be made small at the telephoto end, the effect of aminiaturization becomes large, since the amount of movement of eachgroup, or load of aberrations correction in the prism component can bemade small.

In the zoom optical system according to the sixteenth invention, it isdesired that the negative lens and the positive lens are cemented in thezoom optical system of the fifteenth invention. By cementing lenses, thetotal length can be shortened. Moreover, the influence due todecentering etc., can also be reduced.

In the zoom optical system of the seventeenth invention, it is desiredthat the second group comprises, in order from an object side, apositive lens, a positive lens, and a negative lens in the zoom opticalsystem according to one of the eleventh to the sixteenth invention. Itis desired that two positive lens and one negative lens are arranged inthe second group in order to correct fully aberration and chromaticaberration on the optical axis. Furthermore, in order to arrange thefront side principal point of the second group at the object side, it isadvantageous to constitute that two positive lenses are arranged at theobject side, and one negative lens is arranged at the image side.

In the zoom optical system of the eighteenth invention, it is desiredthat a lens surface at utmost object side in the second group is adouble aspherical lens formed by a plastic molding processing, and apositive lens and a negative lens arranged nearer at an image side, thana lens arranged utmost the object side at the second group are lenseshaving refractive index of 1.7 or more in a zoom optical system of theseventeenth invention. If required functions for correction by anaspherical surface are concentrated on a lens at the object side, and itis constituted by a plastic-mould lens, cost and productivity becomesadvantageous. Moreover, cost and productivity also become advantageous,if required functions for raising a refractive index are concentrated ona lens at the image side, and the positive lens and the negative lens atthe image side are spherical lenses. Furthermore, it is desired that thepositive lens and the negative lens at the image side are formed as acemented lens. Moreover, if the cemented lens is a spherical lens ofglass, a range of selection of refractive index and dispersion can beextended, and correction can make good. The Petzval sum and chromaticaberration which are difficult in correction for a plastic lens can becarried out well. That is, if a plastic lens having an asphericalsurface, and a spherical lens of glass having a high refractive indexare combined like the present invention, highly efficient andadvantageous optical system in cost or processability can beconstituted.

In the zoom optical system according to the nineteenth invention, it isdesired that the fourth group is constituted with one positive lens inone of the zoom optical system of the second to fourth inventions or theeleventh to eighteenth inventions. It is desired that if the fourthgroup is constituted with one positive lens, miniaturization such asshortening of optical total length can be achieved.

Especially, in a zoom optical system of the third invention, it isdesired that if the fourth group is constituted with one positive lens,it becomes unnecessary to arrange two surfaces by combining individuallythe two surfaces where the degrees of aspherical surfaces are large, andaccordingly an arrangement error does not generate.

In addition to these mentioned above, in a zoom optical system of thepresent invention, focusing can be carried out only one group of thesecond group, the third-group, or the fourth group.

It is desired that the first group remains fixed at the time of zoomingand focusing.

It is desired that the fourth group remains fixed at the time ofzooming.

Moreover, the fourth group is moved or may remain fixed when focusing iscarried out.

Further, it is desired that the prism component has only one reflectingsurface.

Furthermore, it is desired that if an image pickup apparatus equippedwith one zoom optical system according to the present invention isconstituted, thinning can be attained fully in the image pickupapparatus, and furthermore, an effect of the zoom optical system whichenables to shorten further more the full length of an optical systemwith a moderate zooming magnification can be acquired.

Hereafter, embodiments of the present invention will be explained usingdrawings.

Embodiment 1

FIG. 1 is a developed view of light path along an optical axis showingan optical arrangement of a zoom of the embodiment 1 according to thepresent invention, and

FIG. 1A shows a state at a wide angle end, FIG. 1B shows a state at amiddle angle position and FIG. 1C shows a telephoto end when aphotographing distance is infinite, respectively.

FIG. 2 is a diagram showing spherical aberration, astigmatism,distortion, chromatic aberration of magnification, and longitudinalaberration at a specific image height with respect to a zoom opticalsystem of the embodiment 1.

FIGS. 2A-2E, 2F-2J, and 2K-2O show the aberrations at a wide angle end,at a middle angle position and, at a telephoto end, respectively wheneach photographing distance is infinite.

FIG. 3 is a diagram showing spherical aberration, astigmatism,distortion, chromatic aberration of magnification, and longitudinalaberration at a specific image height with respect to a zoom opticalsystem of the embodiment 1.

FIGS. 3A-3E, 3F-3J, and 3K-3O show the aberrations at a wide angle end,a middle position and a telephoto end, respectively, when eachphotographing distance is 300 mm as a very close distance.

In FIGS. 2 and 3, IH represents image height.

In FIG. 1, for convenience sake, although the prism component is shownby a straight forward transmitting system which does not bend an opticalpath, it has a reflecting plane where an optical axis is reflected by90° as shown in FIGS. 18, 21, and 23C.

A zoom optical system 1 of the embodiment 1 comprises a first group G1,a second group G2, a third group G3, and a fourth group G4. In FIG. 1, Sis an aperture stop, FL is a parallel plate such as a cover glass of alow pass filter or an electronic image pickup element, an infrared cutfilter, and IM is a light receiving surface of an electronic imagepickup element. In the present embodiment and other embodiments, thesize of the light receiving surface IM and the size of an effectiveimage pickup surface are the same, and the diagonal direction of thesurface is shown in the FIGS.

The first group G1 comprises, in an order from the object side, a prismP, and a cemented lens having a double concave lens L11 and a positivemeniscus lens L12 having a convex surface directed toward the objectside, and it has negative refracting power as a whole. The prism P isarranged at the utmost object side, and it is constituted by comprisingan entrance surface P1 having a concave surface directed toward theobject side, a reflecting surface (illustration is omitted), and an exitsurface P3 having a convex directed toward the image side, and it hasnegative refracting power as a whole. The entrance surface P1 and theexit surface P3 consist of aspherical surfaces having a form whererefracting power becomes weak as each of the surfaces departs from theoptical axis. The reflecting surface (illustration is omitted) consistsof plane, substantially.

The second group G2 comprises, an aperture-stop S, a lens L21 having adouble convex surface on the optical axis, a cemented lens having adouble convex lens L22 and a double concave lens L23, and it hasnegative refracting power as a whole. A lens L21 is formed by a plasticmould, and has an aspherical surface on both sides. The cemented lens ofthe double convex lens L22 and the double concave lens L23 is formed asa glass spherical surface lens.

The third group G3 consists of single a double concave lens L31. Thedouble concave lens L31 is formed by a plastic mould, and has anaspherical surface on both sides. The fourth group G4 consists of singledouble convex lens L41 on the optical axis. As for the lens L41, bothsides are formed aspherical surfaces (equivalent to the asphericalsurfaces a and b in the present invention). The surface at the imageside of the lens L41 (equivalent to the aspherical surface b in thepresent invention) is formed so that it may have the point of inflectionand may become a convex surface toward the image side near the opticalaxis.

When zooming is carried out from a wide angle end to a telephoto end,the first group G1 is fixed, the second group G2 is moved toward theobject side so that a distance to the first group G1 may decrease, thethird group G3 is moved toward the object side so that an distance tothe second group G2 and a distance to the fourth group G4 may increase,respectively, and the fourth group remains fixed. Focusing is carriedout by changing an interval between the second group G2 and the thirdgroup G3. When focusing which is carried out toward a very neardirection from the infinite distance is based, it is constituted so thatthe second group G2 is moved greatly compared with the third group G3 atthe wide angle side, and the third group G3 is moved greatly comparedwith the second group G2 at the telephoto side. Here, the first group G1remains fixed at the time of the focusing. Further, the lens systemwhich is constituted by lenses from the cemented lens having the doubleconcave lens L11 in the first group G1 and the positive meniscus lensL12 having the convex surface directed toward the object side to thelens L41 of the fourth group G4 has positive refracting power as awhole.

Numerical data of the zoom optical system of the embodiment 1 are shownbelow. Here, r₁, r₂ . . . represent a radius of curvature of each-lenssurface, and d₁, d₂ . . . represent a distance between each lenssurface, and na1, na2 . . . represent a refracting index of each lens atd ray, ν_(d1), ν_(d2) . . . is Abbe number of each lens at d ray, andFno is an F number. An aspherical surface is expressed by the followingformula (c), where a direction of an optical axis is Z, a directionwhich intersects perpendicularly to the optical axis is Y, a conecoefficient is k, and an aspherical coefficient is set to A₄, A₆, A₈,and A₁₀,Z=(Y ² /r)/[1+{1−(1+k)·(Y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y¹⁰  (c)

Furthermore, in the numerical data, (AP) represents an asphericalsurface, (AS) represents an aperture stop, and (IM) represents a lightreceiving surface of a image pickup element.

These symbols are common in the numerical data of embodiments to bedescribed later.

Numerical data 1 (Embodiment 1) r₁ = −7.3661 (AP) d₁ = 6.00 n_(d1) =1.52542 ν_(d1) = 55.78 r₂ = −15.8354 (AP) d₂ = 0.21 r₃ = −9.8122 d₃ =0.65 n_(d3) = 1.80400 ν_(d3) = 46.57 r₄ = 13.8961 d₄ = 0.90 n_(d4) =1.84666 ν_(d4) = 23.78 r₅ = 240.4001 d₅ = D5 r₆ = ∞ (AS) d₆ = 0.65 r₇ =4.0914 (AP) d₇ = 2.20 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −20.7730 (AP)d₈ = 0.25 r₉ = 17.2752 d₉ = 1.26 n_(d9) = 1.80400 ν_(d9) = 46.57 r₁₀ =−6.6689 d₁₀ = 0.82 n_(d10) = 1.84666 ν_(d10) = 23.78 r₁₁ = 51.4108 d₁₁ =D11 r₁₂ = −11.0035 (AP) d₁₂ = 1.22 n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃= 4.0986 (AP) d₁₃ = D13 r₁₄ = 27.1190 (AP) d₁₄ = 2.57 n_(d14) = 1.52542ν_(d14) = 55.78 r₁₅ = −3.6438 (AP) d₁₅ = 0.54 r₁₆ = ∞ d₁₆ = 0.50 n_(d16)= 1.51633 ν_(d16) = 64.14 r₁₇ = ∞ d₁₇ = 0.58 r₁₈ = ∞ (IM) Asphericalcoefficient Surface Number k A₄ A₆ A₈ A₁₀ 1 −0.000 1.1835 × 10⁻³ −4.6222× 10⁻⁵ 3.1110 × 10⁻⁶ −6.7350 × 10⁻⁸ 2 −0.000 9.5004 × 10⁻⁴ −1.1680 ×10⁻⁴ 1.8911 × 10⁻⁵ −7.8809 × 10⁻⁷ 7 −0.000 7.1998 × 10⁻⁴   1.0941 × 10⁻⁴2.0647 × 10⁻⁵   2.2314 × 10⁻⁶ 8 −0.000 3.7583 × 10⁻³   6.2853 × 10⁻⁴−9.8635 × 10⁻⁵     2.6799 × 10⁻⁵ 12 −0.000 2.5142 × 10⁻³ −3.4809 × 10⁻⁴13 −0.000 6.7535 × 10⁻³   6.0145 × 10⁻⁵ −5.4357 × 10⁻⁵   14 −0.0001.6783 × 10⁻³   1.9069 × 10⁻⁴ −5.6697 × 10⁻⁷   15 −0.000 1.3251 × 10⁻²−9.0528 × 10⁻⁴ 6.9564 × 10⁻⁵ (AP): an aspherical surface (AS)): anaperture stop (IM): a light receiving surface of a image pickup element

TABLE 1 Focal distance 5 8.5 14.7 Fno 3.1 4.3 5.7 Photographied D5 7.093.89 0.55 distance: D11 2.69 3.05 4.81 infinity D13 1.49 4.33 5.90Photographied D5 7.04 3.89 0.55 distance: D11 2.74 3.13 5.01 300 mm D131.49 4.25 5.71

Embodiment 2

FIG. 4 is a developed view of light path along an optical axis showingan optical arrangement of a zoom optical system of the embodiment 2according to the present invention, and FIG. 4A shows a state at a wideangle end, FIG. 4B shows a state at a middle angle position and FIG. 4Cshows a telephoto end when a photographing distance is infinite,respectively. FIG. 5 is a diagram showing spherical aberration,astigmatism, distortion, chromatic aberration of magnification, andlongitudinal aberration at a specific image height with respect to thezoom optical system of the embodiment 2, and FIGS. 5A-5E, 5F-5J, and5K-5O show the aberrations at a wide angle end, at a middle angleposition and, at a telephoto end respectively, when each photographingdistance is infinite. FIG. 6 is a diagram showing spherical aberration,astigmatism, distortion, chromatic aberration of magnification, andlongitudinal aberration at a specific image height with respect to thezoom optical system of the embodiment 2. FIGS. 6A-6E, 3F-3J, and 3K-3Oshow the aberrations at a wide angle end, a middle position and atelephoto end, respectively, when each photographing distance is 300 mmas a very close distance. IH is image height in FIGS. 5 and 6. In FIG.4, for convenience sake, although the prism component is shown by astraight forward transmitting system which does not bend an opticalpath, it has a reflecting plane where an optical axis is reflected by90° as shown in FIGS. 18, 21, and 23C

The zoom optical system 1 of Embodiment 2 comprises the first group G1,the second group G2, the third group G3, and the fourth group G4. InFIG. 4, S is an aperture stop, FL is a parallel plate such as a coverglass of a low pass filter or an electronic image pickup element, aninfrared cut filter, and IM is a light receiving surface of anelectronic image pickup element.

The first group G1 comprises, in an order from the object side, a prismP, a cemented lens having a double concave lens L11 and a positivemeniscus lens L12 having a convex surface directed toward the objectside, and it has negative refracting power as a whole. The prism P isarranged at the utmost object side, and comprises an entrance surface P1having a concave surface directed toward the object side, a reflectingsurface (illustration is omitted), and an exit surface P3′ havingplane-shape, and it has negative refracting power as a whole. Theentrance surface P1 is formed to be an aspherical surface. Thereflecting surface (illustration is omitted) is formed to be a plane,substantially.

The second group G2 comprises, an aperture-stop S, a lens L21 having adouble convex surface on the optical axis, a cemented lens having adouble convex lens L22 and a double concave lens L23, and it hasnegative refracting power as a whole. A lens L21 is formed by a plasticmould, and has an aspherical surface on both sides. The cemented lens ofthe double convex lens L22 and the double concave lens L23 is formed asa glass spherical surface lens.

The third group G3 consists of single double concave lens L31. Thedouble concave lens L31 is formed by a plastic mould, and has anaspherical surface on both sides.

The fourth group G4 consists of single double convex lens L41 on theoptical axis. As for the lens L41, both sides are formed asphericalsurfaces (equivalent to the aspherical surfaces a and b in the presentinvention). The surface at the image side of the lens L41 (equivalent tothe aspherical surface b in the present invention) is formed so that itmay have the point of inflection and may become a convex surface towardthe image side near the optical axis.

When zooming is carried out from a wide angle end to a telephoto end,the first group G1 is fixed, the second group G2 is moved toward theobject side so that a distance to the first group G1 may be narrowed,the third group G3 is moved toward the object side so that an distanceto the second group G2 and a distance to the fourth group G4 mayincrease, respectively, and the fourth group remains fixed. Focusing iscarried out by changing an interval between the second group G2 and thethird group G3. When focusing which is carried out toward a very neardirection from the infinite distance is based, the second group G2 ismoved greatly compared with the third group G3 at the wide angle side,and the third group G3 is moved greatly compared with the second groupG2 at the telephoto side. Here, the first group G1 remains fixed whenfocusing is carried out. Further, the lens system which is constitutedby lenses from the cemented lens having the double concave lens L11 inthe first group G1 and the positive meniscus lens L12 having the convexsurface directed toward the object side to the lens L41 of the fourthgroup G4 has positive refracting power as a whole.

Numerical data of the zoom optical system of the embodiment 2 are shownbelow.

Numerical data 2 (Embodiment 2) r₁ = −7.6995 (AP) d₁ = 6.00 n_(d1) =1.52542 ν_(d1) = 55.78 r₂ = ∞ d₂ = 0.20 r₃ = −27.5310 d₃ = 0.65 n_(d3) =1.80400 ν_(d3) = 46.57 r₄ = 14.8877 d₄ = 0.86 n_(d4) = 1.84666 ν_(d4) =23.78 r₅ = 93.3267 d₅ = D5 r₆ = ∞ (AS) d₆ = 0.14 r₇ = 3.9288 (AP) d₇ =1.99 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −22.7877 (AP) d₈ = 0.10 r₉ =19.5924 d₉ = 1.33 n_(d9) = 1.80400 ν_(d9) = 46.57 r₁₀ = −6.8623 d₁₀ =0.80 n_(d10) = 1.84666 ν_(d10) = 23.78 r₁₁ = 38.1449 d₁₁ = D11 r₁₂ =−352.5316 (AP) d₁₂ = 0.77 n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃ = 3.5045(AP) d₁₃ = D13 r₁₄ = 69.0396 (AP) d₁₄ = 2.50 n_(d14) = 1.52542 ν_(d14) =55.78 r₁₅ = −3.6244 (AP) d₁₅ = 0.80 r₁₆ = ∞ d₁₆ = 0.50 n_(d16) = 1.51633ν_(d16) = 64.14 r₁₇ = ∞ d₁₇ = 0.54 r₁₈ = ∞ (IM) Aspherical coefficientSurface Number k A₄ A₆ A₈ A₁₀ 1 −0.000 4.2351 × 10⁻⁴ −4.4996 × 10⁻⁵  4.9179 × 10⁻⁶ −1.6629 × 10⁻⁷   7 −0.000 9.0647 × 10⁻⁴ 2.7807 × 10⁻⁴4.2152 × 10⁻⁶ 7.3690 × 10⁻⁶ 8 −0.000 4.8399 × 10⁻³ 6.7470 × 10⁻⁴ −7.9509× 10⁻⁵   3.9980 × 10⁻⁵ 12 −0.000 2.3184 × 10⁻³ −1.9862 × 10⁻⁴   13−0.000 4.6978 × 10⁻³ 2.4867 × 10⁻⁴ −8.6627 × 10⁻⁵   14 −0.000 4.0769 ×10⁻³ 1.6742 × 10⁻⁴ 2.6227 × 10⁻⁶ 15 −0.000 1.5729 × 10⁻² −9.8093 ×10⁻⁴   9.4002 × 10⁻⁵

TABLE 2 Focal distance 5 8.2 14.9 Fno 3.1 4.3 6 Photographied D5 6.993.95 0.20 distance: D11 2.85 2.86 4.44 infinity D13 0.97 3.99 6.16Photographied D5 6.93 3.95 0.20 distance: D11 2.91 2.97 4.69 300 mm D130.97 3.89 5.91

Embodiment 3

FIG. 7 is a developed view of light path along an optical axis showingan optical arrangement of a zoom optical system of the embodiment 3according to the present invention, and FIG. 7A shows a state at a wideangle end, FIG. 7B shows a state at a middle angle position and FIG. 7Cshows a telephoto end when a photographing distance is infinite,respectively. FIG. 5 is a diagram showing spherical aberration,astigmatism, distortion, chromatic aberration of magnification, andlongitudinal aberration at a specific image height with respect to thezoom optical system of the embodiment 2, and FIGS. 8A-8E, 8F-8J, and8K-8O show the aberrations at a wide angle end, at a middle angleposition and, at a telephoto end respectively, when each photographingdistance is infinite. FIG. 9 is a diagram showing spherical aberration,astigmatism, distortion, chromatic aberration of magnification, andlongitudinal aberration at a specific image height with respect to thezoom optical system of the embodiment 2. FIGS. 9A-9E, 9F-9J, and 9K-9Oshow the aberrations at a wide angle end, a middle position and atelephoto end, respectively, when each photographing distance is 300 mmas a very close distance. IH is image height in FIGS. 8 and 9. In FIG.7, for convenience sake, although the prism component is shown by astraight forward transmitting system which does not bend an opticalpath, it has a reflecting plane where an optical axis is reflected by90° as shown in FIGS. 18, 21, and 23C.

The zoom optical system 1 of embodiment 3 comprises the first group G1,the second group G2, the third group G3, and the fourth group G4. InFIG. 7, S is an aperture stop, FL is a parallel plate such as a coverglass of a low pass filter or an electronic image pickup element, aninfrared cut filter, and IM is a light receiving surface of anelectronic image pickup element.

The first group G1 comprises, in order from the object side, a prism P,a cemented lens having a double concave lens L11 and a positive meniscuslens L12 having a convex surface directed toward the object side, and ithas negative refracting power as a whole. The prism P is arranged at theutmost object side, and it is constituted by comprising an entrancesurface P1 having a concave surface directed toward the object side, areflecting surface (illustration is omitted), and an exit surface P3′having a plane-shape, and it has negative refracting power as a whole.The entrance surface P1 is formed to be an aspherical surface. Thereflecting surface (illustration is omitted) consists of plane,substantially.

The second group G2 comprises, an aperture-stop S, a lens L21 having adouble convex surface on the optical axis, a cemented lens having adouble convex lens L22 and a double concave lens L23, and it hasnegative refracting power as a whole. A lens L21 is formed by a plasticmould, and both surfaces are aspherical. The cemented lens of the doubleconvex lens L22 and the double concave lens L23 is formed as a glassspherical surface lens.

The third group G3 consists of single negative meniscus lens L31′ havinga convex surface directed toward the object side. The negative meniscuslens L31′ is formed by a plastic mould, and the both surfaces are formedto be aspherical surfaces.

In the zoom optical system 1 of embodiment 3, between a lens surface atthe image side in the second group G2 and a lens surface at utmostobject side in the third group, a well-known liquid crystal shutter isarranged as a light quantity adjustment mechanism SH (in FIG. 7, anillustration is omitted). As a light quantity adjustment mechanism SH,it is possible to use a liquid crystal shutter in which a liquid crystalchanges transmission of light electrically as shown in the presentembodiment etc., a mechanical shutter mechanism, a mechanism in which aND filter can be inserted and can be pulled out, or other mechanismcombined them mentioned above.

The fourth group G4 consists of single double convex lens L41 on theoptical axis. As for the lens L41, both sides are formed asphericalsurfaces (equivalent to the aspherical surfaces a and b in the presentinvention). The surface at the image side of the lens L41 (equivalent tothe aspherical surface b in the present invention) is formed so that itmay have the point of inflection and may become a convex surface towardthe image side near the optical axis.

When zooming is carried out from a wide angle end to a telephoto end,the first group G1 is fixed, the second group G2 is moved toward theobject side so that a distance to the first group G1 may decrease, thethird group G3 is moved toward the object side so that an distance tothe second group G2 and a distance to the fourth group G4 may increase,respectively, and the fourth group remains fixed. Focusing is carriedout by changing an interval between the second group G2 and the thirdgroup G3. When focusing which is carried out toward a very neardirection from the infinite distance is based, the second group G2 ismoved greatly compared with the third group G3 at the wide angle side,and the third group G3 is moved greatly compared with the second groupG2 at the telephoto side. Here, the first group G1 remains fixed whenfocusing is carried out. Further, the lens system which is constitutedby lenses from the cemented lens having the double concave lens L11 andthe double concave lens L12 to the lens L41 of the fourth group G4 haspositive refracting power as a whole.

Numerical data of the zoom optical system of the embodiment 3 are shownbelow.

Numerical data 3 (Embodiment 3) r₁ = −7.7334 (AP) d₁ = 6.00 n_(d1) =1.52542 ν_(d1) = 55.78 r₂ = ∞ d₂ = 0.20 r₃ = −26.6932 d₃ = 0.65 n_(d3) =1.80400 ν_(d3) = 46.57 r₄ = 14.5085 d₄ = 0.87 n_(d4) = 1.84666 ν_(d4) =23.78 r₅ = 99.8567 d₅ = D5 r₆ = ∞ (AS) d₆ = 0.14 r₇ = 3.9235 (AP) d₇ =1.99 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −22.8668 (AP) d₈ = 0.10 r₉ =19.6534 d₉ = 1.33 n_(d9) = 1.80400 ν_(d9) = 46.57 r₁₀ = −6.8845 d₁₀ =0.80 n_(d10) = 1.84666 ν_(d10) = 23.78 r₁₁ = 37.8553 d₁₁ = 0.50 r₁₂ = ∞d₁₂ = 1.00 n_(d12) = 1.51633 ν_(d12) = 64.14 r₁₃ = ∞ d₁₃ = D13 r₁₄ =949.9402 (AP) d₁₄ = 0.77 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = 3.4651(AP) d₁₅ = D15 r₁₆ = 97.7468 (AP) d₁₆ = 2.53 n_(d16) = 1.52542 ν_(d16) =55.78 r₁₇ = −3.5526 d₁₇ = 0.80 r₁₈ = ∞ d₁₈ = 0.50 n_(d18) = 1.51633ν_(d18) = 64.14 r₁₉ = ∞ d₁₉ = 0.55 r₂₀ = ∞ (IM) Aspherical coefficientSurface Number k A₄ A₆ A₈ A₁₀ 1 −0.000 3.3769 × 10⁻⁴ −2.4237 × 10⁻⁵    3.1079 × 10⁻⁶ −1.0918 × 10⁻⁷   7 −0.000 1.0092 × 10⁻³ 3.2198 × 10⁻⁴−8.5427 × 10⁻⁶ 9.1174 × 10⁻⁶ 8 −0.000 4.9588 × 10⁻³ 7.7360 × 10⁻⁴−1.1630 × 10⁻⁴ 4.7068 × 10⁻⁵ 14 −0.000 1.5126 × 10⁻³ −1.5107 × 10⁻⁴   15−0.000 3.5741 × 10⁻³ 2.4750 × 10⁻⁴ −8.7786 × 10⁻⁵ 16 −0.000 3.6318 ×10⁻³ 2.3999 × 10⁻⁴ −2.0159 × 10⁻⁶ 17 −0.000 1.5224 × 10⁻² −8.5997 ×10⁻⁴     8.8017 × 10⁻⁵

TABLE 3 Focal distance 5 8.2 14.9 Fno 3.1 4.3 6 Photographied D5 6.993.95 0.20 distance: D13 1.69 1.70 3.28 infinity D15 0.95 3.97 6.14Photographied D5 6.92 3.95 0.20 distance D13 1.75 1.81 3.54 300 mm D150.95 3.86 5.89

Embodiment 4

FIG. 10 is a developed view of light path along an optical axis showingan optical arrangement of a zoom of the embodiment 1 according to thepresent invention, and FIG. 10A shows a state at a wide angle end, FIG.1B shows a state at a middle angle position and FIG. 1C shows atelephoto end when a photographing distance is infinite, respectively.FIG. 11 is a diagram showing spherical aberration, astigmatism,distortion, chromatic aberration of magnification, and longitudinalaberration at a specific image height with respect to a zoom opticalsystem of the embodiment 1, and

FIGS. 11A-11E, 11F-11J, and 11K-11O show the aberrations at a wide angleend, at a middle angle position and, at a telephoto end respectively,when each photographing distance is infinite. FIG. 12 is a diagramshowing spherical aberration, astigmatism, distortion, chromaticaberration of magnification, and longitudinal aberration at a specificimage height with respect to a zoom optical system of the embodiment 4,and FIGS. 12A-12E, 11F-12J, and 12K-12O show the aberrations at a wideangle end, a middle position and a telephoto end, respectively, wheneach photographing distance is 300 mm as a very close distance. IH isimage height in FIGS. 11 and 12. In FIG. 10, for convenience sake,although the prism component is shown by a straight forward transmittingsystem which does not bend an optical path, it has a reflecting planewhere an optical axis is reflected by 90° as shown in FIGS. 18, 21, and23C.

The zoom optical system 1 of embodiment 4 comprises the first group G1,the second group G2, the third group G3, and the fourth group G4. InFIG. 10, S is an aperture stop, FL is a parallel plate such as a coverglass of a low pass filter or an electronic image pickup element, aninfrared cut filter, and IM is a light receiving surface of anelectronic image pickup element.

The first group G1 comprises, in an order from the object side, a prismP, a cemented lens having a double concave lens L11 and a double convexlens L12′, and it has negative refracting power as a whole. The prism Pis arranged at the utmost object side, and comprises an entrance surfaceP1 having a concave surface directed toward the object side, areflecting surface (illustration is omitted), and an exit surface P3having a convex surface directed toward the image side on the opticalaxis, and it has negative refracting power as a whole. The entrancesurface P1 and the exit surface P3 consist of aspherical surfaces havinga form where refracting power becomes weak as each of the surfacesdeparts from the optical axis. The reflecting surface (illustration isomitted) consists of plane, substantially.

The second group G2 comprises, an aperture-stop S, a lens L21 having adouble convex surface on the optical axis, a cemented lens having adouble convex lens L22 and a double concave lens L23, and it hasnegative refracting power as a whole. A lens L21 is formed by a plasticmould, and has an aspherical surface on both sides. The cemented lens ofthe double convex lens L22 and the double concave lens L23 is formed asa glass spherical surface lens.

The third group G3 consists of single a double concave lens L31. Thedouble concave lens L31 is formed by a plastic mould, and has anaspherical surface on both sides. The fourth group G4 consists of singledouble convex lens L41 on the optical axis. As for the lens L41, bothsides are formed aspherical surfaces (equivalent to the asphericalsurfaces a and b in the present invention). The surface at the imageside of the lens L41 (equivalent to the aspherical surface b in thepresent invention) is formed so that it may have the point of inflectionand may become a convex surface toward the image side near the opticalaxis.

When zooming is carried out from a wide angle end to a telephoto end,the first group G1 is fixed, the second group G2 is moved toward theobject side so that a distance to the first group G1 may decrease, thethird group G3 is moved toward the object side so that an distance tothe second group G2 and a distance to the fourth group G4 may increase,respectively, and the fourth group remains fixed. Focusing is carriedout by changing an interval between the second group G2 and the thirdgroup G3. When focusing which is carried out toward a very neardirection from the infinite distance is based, the second group G2 ismoved greatly compared with the third group G3 at the wide angle side,and the third group G3 is moved greatly compared with the second groupG2 at the telephoto end. Here, the first group G1 remains fixed whenfocusing is carried out. Further, the lens system which is constitutedby lenses from the cemented lens having the double concave lens L11 andthe double concave lens L12′ to the lens L41 of the fourth group G4 haspositive refracting power as a whole.

Numerical data of the zoom optical system of the embodiment 4 are shownbelow.

Numerical data 4 (Embodiment 4) r₁ = −7.2950 (AP) d₁ = 6.00 n_(d1) =1.52542 ν_(d1) = 55.78 r₂ = −16.7915 (AP) d₂ = 0.36 r₃ = −9.7309 d₃ =0.66 n_(d3) = 1.80400 ν_(d3) = 46.57 r₄ = 13.5503 d₄ = 0.95 n_(d4) =1.84666 ν_(d4) = 23.78 r₅ = −1219.4911 d₅ = D5 r₆ = ∞ (AS) d₆ = 0.30 r₇= 4.0499 (AP) d₇ = 2.06 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −21.5703(AP) d₈ = 0.12 r₉ = 16.6160 d₉ = 1.25 n_(d9) = 1.80400 ν_(d9) = 46.57r₁₀ = −6.3712 d₁₀ = 0.80 n_(d10) = 1.84666 ν_(d10) = 23.78 r₁₁ = 77.1776d₁₁ = D11 r₁₂ = −10.6390 (AP) d₁₂ = 1.07 n_(d12) = 1.52542 ν_(d12) =55.78 r₁₃ = 3.9135 (AP) d₁₃ = D13 r₁₄ = 20.8952 (AP) d₁₄ = 2.55 n_(d14)= 1.52542 ν_(d14) = 55.78 r₁₅ = −3.7887 (AP) d₁₅ = 0.59 r₁₆ = ∞ d₁₆ =0.50 n_(d16) = 1.51633 ν_(d16) = 64.14 r₁₇ = ∞ d₁₇ = 0.60 r₁₈ = ∞ (IM)Aspherical coefficient Surface Number k A₄ A₆ A₈ A₁₀ 1 −0.000 1.2734 ×10⁻³ −3.7071 × 10⁻⁵ 1.5959 × 10⁻⁶ −1.1269 × 10⁻⁸ 2 −0.000 1.0379 × 10⁻³−1.0413 × 10⁻⁴ 1.5254 × 10⁻⁵ −4.8660 × 10⁻⁷ 7 −0.000 9.9710 × 10⁻⁴  1.3954 × 10⁻⁴ 1.9959 × 10⁻⁵   3.3621 × 10⁻⁶ 8 −0.000 4.3607 × 10⁻³  4.3558 × 10⁻⁴ −2.1370 × 10⁻⁵     2.1064 × 10⁻⁵ 12 −0.000 4.6291 × 10⁻³−1.1680 × 10⁻³ 13 −0.000 9.0463 × 10⁻³ −6.8653 × 10⁻⁴ −8.7660 × 10⁻⁵  14 −0.000 2.5318 × 10⁻³ −9.3395 × 10⁻⁵ 1.6074 × 10⁻⁵ −2.1482 × 10⁻⁷ 15−0.000 1.3685 × 10⁻² −1.2063 × 10⁻³ −7.7094 × 10⁻⁵  

TABLE 4 Focal distance 5 8.5 14.7 Fno 3.1 4.3 5.7 Photographied D5 6.723.56 0.32 distance: D11 2.71 3.07 4.75 infinity D13 1.43 4.23 5.79Photographied D5 6.68 3.56 0.32 distance D11 2.76 3.15 4.94 300 mm D131.43 4.14 5.60

Embodiment 5

FIG. 13 is a developed view of light path along an optical axis showingan optical arrangement of a zoom of the embodiment 5 according to thepresent invention, and FIG. 13A shows a state at a wide angle end, FIG.13B shows a state at a middle angle position and FIG. 13C shows atelephoto end when a photographing distance is infinite, respectively.FIG. 14 is a diagram showing spherical aberration, astigmatism,distortion, chromatic aberration of magnification, and longitudinalaberration at a specific image height with respect to a zoom opticalsystem of the embodiment 5, and FIGS. 14A-14E, 14F-14J, and 14K-14O showthe aberrations at a wide angle end, at a middle angle position and, ata telephoto end respectively, when each photographing distance isinfinite. FIG. 15 is a diagram showing spherical aberration,astigmatism, distortion, chromatic aberration of magnification, andlongitudinal aberration at a specific image height with respect to azoom optical system of the embodiment 5, and FIGS. 15A-15E, 15F-15J, and15K-15O show the aberrations at a wide angle end, a middle position anda telephoto end respectively, when each photographing distance is 300 mmas a very close distance. IH is image height in FIGS. 14 and 15. In FIG.13, for convenience sake, although the prism component is shown by astraight forward transmitting system which does not bend an opticalpath, it has a reflecting plane where an optical axis is reflected by90° as shown in FIGS. 18, 21, and 23C.

The zoom optical system 1 of embodiment 5 comprises the first group G1,the second group G2, the third group G3, and the fourth group G4. InFIG. 13, S is an aperture stop, FL is a parallel plate such as a coverglass of a low pass filter or an electronic image pickup element, aninfrared cut filter, and IM is a light receiving surface of anelectronic image pickup element.

The first group G1 comprises, in an order from the object side, a prismP, a cemented lens having a double concave lens L11 and a double convexlens L12′, and it has negative refracting power as a whole. The prism Pis arranged at the utmost object side, and it is constituted bycomprising an entrance surface P1 having a concave surface directedtoward the object side, a reflecting surface (illustration is omitted),and an exit surface P3 having a convex directed toward the image side,and The entrance surface P1 and the exit surface P3 consist ofaspherical surfaces having a form where refracting power becomes weak aseach of the surfaces departs from the optical axis. The reflectingsurface (illustration is omitted) consists of plane, substantially.

The second group G2 comprises, an aperture-stop S, a lens L21 having adouble convex surface on the optical axis, a cemented lens having adouble convex lens L22 and a negative meniscus lens L23′ having aconcave surface directed toward the object side, and it has negativerefracting power as a whole. A lens L21 is formed by a plastic mould,and has an aspherical surface on both sides. The cemented lens of thedouble convex lens L22 and the negative meniscus lens L23′ having aconcave surface directed to the object side, is formed as a glassspherical surface lens.

The third group G3 consists of single a double concave lens L31. Thedouble concave lens L31 is formed by a plastic mould, and has anaspherical surface at the object side.

The fourth group G4 consists of single double convex lens L41 on theoptical axis. As for the lens L41, both sides are formed asphericalsurfaces (equivalent to the aspherical surfaces a and b in the presentinvention). The surface at the image side of the lens L41 (equivalent tothe aspherical surface b in the present invention) is formed so that itmay have the point of inflection and may become a convex surface towardthe image side near the optical axis.

When zooming is carried out from a wide angle end to a telephoto end,the first group G1 remains fixed, the second group G2 is moved towardthe object side so that a distance to the first group G1 may decrease,the third group G3 is moved toward the object side so that an distanceto the second group G2 and a distance to the fourth group G4 mayincrease, respectively, and the fourth group remains fixed. Focusing iscarried out by changing an interval between the second group G2 and thethird group G3. When focusing which is carried out toward a very neardirection from the infinite distance is based, the second group G2 ismoved greatly compared with the third group G3 at the wide angle side,and the third group G3 is moved greatly compared with the second groupG2 at the telephoto end. Here, the first group G1 remains fixed whenfocusing is carried out.

Further, the lens system which is constituted by lenses from thecemented lens having the double concave lens L11 and the double convexlens L12′ of the first group to the lens L41 of the fourth group G4 haspositive refracting power as a whole.

Numerical data of the image forming optical system of the embodiment 5are shown below.

Numerical data 5 (Embodiment 5) r₁ = −8.4605 (AP) d₁ = 6.00 n_(d1) =1.80400 ν_(d1) = 46.57 r₂ = −58.9999 (AP) d₂ = 0.13 r₃ = −25.1357 d₃ =0.65 n_(d3) = 1.80400 ν_(d3) = 46.57 r₄ = 16.4035 d₄ = 0.94 n_(d4) =1.84666 ν_(d4) = 23.78 r₅ = −276.3763 d₅ = D5 r₆ = ∞ (AS) d₆ = 0.23 r₇ =4.2908 (AP) d₇ = 2.33 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = 769.3655 (AP)d₈ = 0.26 r₉ = 35.3764 d₉ = 1.66 n_(d9) = 1.80400 ν_(d9) = 46.57 r₁₀ =−4.5478 d₁₀ = 0.65 n_(d10) = 1.84666 ν_(d10) = 23.78 r₁₁ = −18.0677 d₁₁= D11 r₁₂ = −10.8542 (AP) d₁₂ = 0.72 n_(d12) = 1.52542 ν_(d12) = 55.78r₁₃ = 3.9342 d₁₃ = D13 r₁₄ = 16.8714 (AP) d₁₄ = 2.52 n_(d14) = 1.52542ν_(d14) = 55.78 r₁₅ = −3.9902 (AP) d₁₅ = 0.67 r₁₆ = ∞ d₁₆ = 0.50 n_(d16)= 1.51633 ν_(d16) = 64.14 r₁₇ = ∞ d₁₇ = 0.55 r₁₈ = ∞ (IM) Asphericalcoefficient Surface Number k A₄ A₆ A₈ A₁₀ A₁₂ 1 −0.000 3.1854 × 10⁻⁴8.1624 × 10⁻⁶ −2.7758 × 10⁻⁷   1.3649 × 10⁻⁸ 2 −0.000 1.6895 × 10⁻⁴1.0091 × 10⁻⁵ 7 −0.000 4.8122 × 10⁻⁴ 5.9923 × 10⁻⁵ 1.7634 × 10⁻⁵ 7.4884× 10⁻⁸ 8 −0.000 3.5049 × 10⁻³ 1.9473 × 10⁻⁴ 2.5412 × 10⁻⁵ 3.8429 × 10⁻⁶12 −0.000 −9.5269 × 10⁻⁴   1.1024 × 10⁻⁵ 14 −0.000 −6.5298 × 10⁻⁴  1.9493 × 10⁻⁴ 1.3236 × 10⁻⁶ 15 −0.000 8.1885 × 10⁻³ −7.2053 × 10⁻⁴  −1.0516 × 10⁻⁴   −5.8514 × 10⁻⁶   1.7832 × 10⁻⁷

TABLE 5 Focal distance 5 8.6 14.9 Fno 3.1 4.4 5.9 Photographied D5 7.994.41 0.58 distance: D11 3.10 3.17 4.26 infinity D13 1.35 4.87 7.60Photographied D5 7.95 4.41 0.58 distance D11 3.15 3.25 4.43 300 mm D131.35 4.79 7.44

Next, values corresponding to numerical parameters of the conditions ineach embodiment are shown.

TABLE 6 Values of conditions in each of the embodiments conditionsembodiment 1 embodiment 2 embodiment 3 embodiment 4 embodiment 5 (1) 1.4< G23W/G34W < 3 1.81 2.94 1.78 1.90 2.30 (2) 0.4 < G23T/G34T < 1.5 0.820.67 0.53 0.82 0.56 (3) 0.08 < (ha11 − ha07)/I < 0.3 0.135 0.179 0.1710.129 0.102 (4) −0.1 < ha07/I < 0.07 0.038 0.035 0.031 0.046 0.041 (5)0.45 < Cb/I < 1 0.743 0.575 0.589 0.857 0.807 (6) −4 < rp1/I < −1.8−2.63 −2.75 −2.76 −2.61 −3.02 (7) 8 < L/I < 12 10.57 10.00 10.13 10.2310.79 (8) 2.5 < M/I < 7 3.91 4.28 4.28 3.84 4.88 (9) −0.55 < φP · fw < 0−0.15 −0.34 −0.34 −0.16 −0.39 (10) −1 < (rp1 − rp2)/(rp1 + rp2) < −0.2−0.36 −1 −1 −0.39 −0.75

In the zoom optical system of the embodiment 1 to the embodiment 6, itis possible to carry out focusing by moving only one of groups of thesecond group G2, the third group G3, and the fourth group G4. Moreover,the fourth group G4 may be moved or may be fixed when focusing iscarried out.

The electronic image pickup apparatus using the optical zoom opticalsystem of the present invention such as that mentioned above can be usedin the photographing apparatus in which the image of the object isformed by the image forming system, such as a zoom optical system, andis received by the image pickup element, such as a CCD, to take aphotograph, notably in a digital camera or a video camera, a personalcomputer which is an example of an information processing apparatus, ora telephone, especially a mobile phone that is handy to carry. Theembodiments of such apparatuses are shown below.

FIGS. 16 to 18, are conceptual diagrams of composition in which the zoomoptical system of the present invention is incorporated in thephotographing optical system 41 of the digital camera 40. FIG. 16 is afront perspective diagram showing the outside view of the digital camera40, FIG. 17 is a back perspective diagram of the same, and FIG. 18 is aninternal block diagram showing the composition of the digital camera 40.The digital camera shown in FIG. 18 is constructed so that an imagepickup optical path is bent along the major side of a finder, and anobserver's eye is viewed from the upper side.

An electronic camera 40, in this example, includes a photographingoptical system 41 constructed as in the embodiment 1 of the presentinvention, having a photographing optical path 42; a finder opticalsystem 43 having a finder optical path 44; a shutter button 45; a flashlamp 46; and a liquid crystal display monitor 47. When the shutterbutton 45 provided on the upper portion of the camera 40 is pushed,photographing is carried out through, for example, the light pathbending optical system of the embodiment 1 which constitutes thephotographing optical system 41 in association with the shutter button45. An object image produced by the photographing optical system 41 isformed on an image pickup surface of CCD 49 through filter LPF such asthe low-pass filter and the infrared cutoff filter and the like and acover glass CG.

The object image received by the CCD 49 is displayed as an electronicimage on the liquid crystal display monitor 47 provided on the backsideof the camera through a processing means 51. A recording means 52 isconnected to the processing means 51, where a photographed electronicimage can be recorded. Also, the recording means may be providedindependently from the processing means 51, or may be constructed sothat the image is electronically recorded and written by a flexibledisk, a memory card, MO and the like. The camera may be constructed as afilm camera using a silver halide film instead of the CCD 49.

Further, a finder objective optical system 53 is arranged on the finderoptical path 44. An object image produced on an image pickup plane 42 ofthe finder objective optical system 53 is formed on a field frame 57through a Porro prism 55 that is an image erecting member. Behind thePorro prism 55 is arranged an eye-piece optical system 59 whichintroduces an erect image into an observer's eye E. Cover members 50 arearranged at the entrance sides of the photographing optical system 41and the finder objective optical system 53 and the exit side of theeyepiece optical system 59 respectively.

The digital camera 40 constituted in this way has an effect in thinningof a camera by having bent a light path to the direction of long side.Furthermore, since the photographing optical system 41 has a highvariable magnification ratio and it is a bright zoom lens optical systemin which aberrations are favorably corrected and a large back-focusspace for filter and the like can be arranged, high performance andfunction can be realized, and miniaturization and low cost productioncan be realized since the photographing optical system 41 can beconstituted with small numbers of optical elements.

Also, the digital camera 40 of the present embodiment may be constructedso that the image pickup optical path is bent along the minor side ofthe finder. In this example of FIG. 18, the plane-parallel plate isarranged as cover component 50. Here, without preparing a covercomponent, a surface arranged at the utmost object side in the opticalsystem of the present invention can be used also as a cover component.In this example, a surface at the utmost object side is used as anentrance surface of the first group G1.

FIG. 19 shows the configuration of the internal circuit of essentialsections of the digital camera 40. In the following description, theprocessing means 51 includes, for example, a CDS/ADC section 24, atemporary memory 17, and an image processing section 18, and therecording means 52 includes, for example, a storage medium section 19and the like.

The digital camera 40′, as shown in FIG. 19, has an operating section12; a control section 13 connected to the operating section 12; and animage drive circuit 16, the temporary memory 17, the image processingsection 18, the storage medium section 19, a display section 20, and apreset information memory section 21, connected to control signal outputports of the control section 13 through busses 14 and 15. The temporarymemory 17, the image processing section 18, the storage medium section19, the display section 20, and the preset information memory section 21are constructed so that data are mutually input or output through a bus22. A CCD 49 and the CDS/ADC section 24 are connected to the image drivecircuit 16.

The operating section 12 is a circuit provided with various inputbuttons and switches and transmitting event information input from theexterior (a camera user) through these input buttons and switches to thecontrol section 13. The control section 13 is a circuit that is acentral arithmetical processing unit including, for example, a CPU, andincorporates a program memory, not shown, to control the whole of thedigital camera 40 by receiving instructions input from the camera userthrough the operating section 12 in accordance with a program housed inthe program memory.

The CCD 49 is an image pickup element that is drive-controlled by theimage drive circuit 16 and converts the amount of light of each pixel ofthe object image into an electric signal to output the signal to theCDS/ADC section 24.

The CDS/ADC section 24 is a circuit that amplifies the electric signalinput from the CCD 49 and carries out an analog/digital conversion tooutput image raw data (Bayer data, hereinafter called RAW data)according to only such amplification and digital conversion to thetemporary memory 17.

The temporary memory 17 is a memory device that is a buffer including,for example, SDRAM and temporarily stores the RAW data output from theCDS/ADC section 24.

The image processing section 18 is a circuit that reads out the RAW datastored in the temporary memory 17 or the storage medium section 19 toelectrically process various images, together with correction for coma,in accordance with image-quality parameters designated by the controlsection 13.

The storage medium section 19 is a control circuit of a device thatremovably mounts a card or stick recording medium including, forexample, a flash memory and records and holds the RAW data transferredfrom the temporary memory 17 and image data processed by the imageprocessing section 18 in the card or stick flash memory.

The display section 20 is a circuit that is provided with the liquidcrystal display monitor 47 to display an image and an operation menu onthe liquid crystal display monitor 47. The preset information memorysection 21 is provided with a ROM previously incorporating variousimage-quality parameters and a RAM storing an image-quality parameterselected by the input operation of the operating section 12 from amongimage-quality parameters read out from the ROM. The preset informationmemory section 21 is a circuit for controlling the input into and outputfrom to these memories.

Subsequently, a personal computer that is an example of an informationprocessing apparatus incorporating the path bending zoom optical systemof the present invention as an objective optical system is illustratedin FIGS. 20-22. FIG. 20 is a front perspective diagram in which a coverof the personal computer 300 is opened, FIG. 21 is a sectional drawingof a photographing optical system 303 incorporated in the personalcomputer 300, and FIG. 22 is a side elevation of FIG. 20.

A personal computer 300, as shown in FIGS. 20-22, has a keyboard 301provided for the purpose that an operator inputs information from theexterior, an information processing means or a recording means,(illustration not shown), a monitor 302 displaying information for theoperator, and a photographing optical system 303 for photographing theoperator himself or surrounding images. Here, the monitor 302 may be atransmission-type liquid crystal display element illuminated withbacklight, (illustration not shown), from the back side, areflection-type liquid crystal display element reflecting light from thefront for display, or a CRT display.

In FIG. 20, the photographing optical system 303 is housed in themonitor 302 upper-right, but it is not limited to this place and may bearranged at any place, such as the periphery of the monitor 302 or ofthe keyboard 301. The photographing optical system 303 has an objectivelens 112 including the path-bending zoom optical system, for example, ofthe embodiment 1 according to the present invention and an image pickupelement chip 162 receiving an image, arranged on a photographing opticalpath 304. These are housed in the personal computer 300.

Here, the cover glass CG is additionally cemented to the image pickupelement chip 162 and they are integrally constructed as an image pickupunit 160. Since the image pickup unit 160 is fitted into the rear end ofa lens frame 113 of the object lens 112 and can be mounted in a singleoperation, the alignment of the objective lens 112 and the chip 162 andthe adjustment of face-to-face spacing are not required and assembly issimplified. At the top (illustration not shown) of the lens frame 113, acover glass 114 for protecting the objective lens 112 is placed. Also,the driving mechanism of the zoom optical system in the lens frame 113is omitted from the figure.

An object image received by the image pickup element chip 162 is inputinto the processing means of the personal computer 300 through aterminal 166 and is displayed as an electronic image on the monitor 302.In FIG. 20, an image 305 photographed by the operator is shown as anexample. It is also possible to display the image 305 on the personalcomputer of a communication mate lying at a remote place through theprocessing means and the internet or the telephone.

Subsequently, a telephone that is an example of an informationprocessing apparatus incorporating the zoom optical system of thepresent invention as a photographing optical system, especially, acellular phone which is convenient for carring is illustrated in FIG.23. FIG. 23A is a front view of the cellular phone 400, FIG. 23B is aside view of the same, and FIG. 23C is a sectional drawing of aphotographing optical system 405.

A mobile phone 400, as shown in FIG. 23, includes a microphone section401 inputting an operator's voice as information; a speaker section 402outputting the voice of a communication mate; input dials 403 that anoperator inputs information; a monitor 404 displaying information, suchas the photographed image of the operator himself or of thecommunication mate and telephone numbers; a photographing optical system405; an antenna 406 transmitting and receiving communication waves; anda processing means (illustration not shown) processing imageinformation, communication information, and input signals.

Here, the monitor 404 is a liquid-crystal-display element. Arrangementand position of each composition are not restricted to only these shownin the figures. This photographing optical system 405 has the objectivelens 112 which is arranged on the photographing optical path 407 andconsists of the light path bending zoom optical system 1 and the imagepickup element chip 162 for receiving light of the object image of theembodiment 1 according to the present invention. These are built in thecellular phone 400.

Here, the cover glass CG is additionally cemented to the imaging elementchip 162 and they are integrally constructed as the image pickup unit160. Since the image pickup unit 160 is fitted into the rear end of thelens frame 113 of the objective lens 112 and can be mounted in a singleoperation, the alignment of the objective lens 112 and the chip 162 andthe adjustment of face-to-face spacing are not required and assembly issimplified. At the top (illustration not shown) of the lens frame 113,the cover glass 114 for protecting the objective lens 112 is placed.Also, the driving mechanism of the zoom optical system in the lens frame113 is omitted from the figure.

An object image received by the image pickup element chip 162 is inputinto the processing means, not shown, through the terminal 166 and isdisplayed as an electronic image on either the monitor 404 or themonitor of the communication mate, or both. Also, the processing meansincludes a signal processing function that when the image is transmittedto the communication mate, the information of the object image receivedby the chip 162 is converted into a transmittable signal.

1. A zoom optical system comprising, in order from an object side: afirst group having negative refracting power; a second group havingpositive refracting power; a third group having negative refractingpower; and a fourth group having positive refracting power; wherein thefirst group comprises a prism component arranged on an utmost objectside and comprising an entrance surface having a concave surfacedirected toward the object side, a reflecting surface and an exitsurface; and wherein the second group comprises an aperture stop;wherein, when zooming is carried out from a wide angle end to atelephoto end, the second group and the third group are moved toward theobject side respectively, an interval between the first group and thesecond group decreases, and an interval between the second group and thethird group and an interval between the third group and the fourth groupincrease respectively; and wherein the following conditions (1) and (2)are satisfied:1.4<G23W/G34W<3  (1)0.4<G23T/G34T<1.5  (2) where G23W is an interval between the secondgroup and the third group at the wide angle end, G34W is an intervalbetween the third group and the fourth group at the wide angle end, G23Tis an interval between the second group and the third group at thetelephoto end, and G34T is an interval between the third group and thefourth group at the telephoto end.
 2. A zoom optical system comprising,in order from an object side: a first group having negative refractingpower; a second group having positive refracting power; a third grouphaving negative refracting power; and a fourth group having positiverefracting power; wherein the first group comprises a prism componentarranged on an utmost object side and comprising an entrance surfacehaving a concave surface directed toward the object side, a reflectingsurface and an exit surface; wherein the second group comprises anaperture stop; wherein, when zooming is carried out from a wide angleend to a telephoto end, the second group and the third group are movedtoward the object side respectively, an interval between the first groupand the second group decreases, and an interval between the second groupand the third group and an interval between the third group and thefourth group increase respectively; and wherein focusing is carried outby changing the interval between the second group and the third group insuch a manner that the second group mainly works in view of a movementamount ratio of the second group to the third group in focusing frominfinity to proximity where zooming condition is fixed to a wide angleside, and that the third group mainly works in view of the movementamount ratio of the second group to the third group in focusing frominfinity to proximity where zooming condition is fixed to a telephotoside.
 3. A zoom optical system comprising, in order from an object side:a first group having negative refracting power; a second group havingpositive refracting power; a third group having negative refractingpower; and a fourth group having positive refracting power; wherein thefirst group comprises a prism component arranged on an utmost objectside and comprising an entrance surface having a concave surfacedirected toward the object side, a reflecting surface and an exitsurface; wherein the second group comprises an aperture stop; wherein,when zooming is carried out from a wide angle end to a telephoto end,the second group and the third group are moved toward the object siderespectively, an interval between the first group and the second groupdecreases, and an interval between the second group and the third groupand an interval between the third group and the fourth group increaserespectively; and wherein the zoom optical system further comprises alight quantity adjustment part arranged between a lens surface arrangedon an utmost image side in the second group and a lens surface arrangedon an utmost object side in the third group.
 4. The zoom optical systemaccording to one of claims 1, 2 and 3, wherein the prism component hasnegative refracting power as a whole.
 5. The zoom optical systemaccording to one of claims 1, 2 and 3, wherein the following condition(9) is satisfied:0.55<ΦP·fw<0  (9) where a refracting power of the prism component is ΦP,and a focal length of the zoom optical system at a wide angle end is fw.6. The zoom optical system according to one of claims 1, 2 and 3 whereinthe following condition (10) is satisfied:−1<(rP1−rP2)/(rP1+rP2)<−0.2  (10) where a paraxial radius of curvatureof the entrance surface of the prism component is rP1, and a paraxialradius of curvature of the exit surface of the prism component is rP2.7. The zoom optical system according to one of claims 1, 2 and 3,wherein the entrance surface and the exit surface of the prism componentare aspherical surfaces, the reflecting surface of the prism componentis a plane surface, and each of the aspherical surfaces of the prismcomponent has a shape such that refracting power becomes weak as itdeparts from an optical axis.
 8. A zoom optical system comprising, inorder from an object side: a prism component which has an entrancesurface having negative refracting power, a reflecting surface, and anexit surface having positive refracting power; and a lens group havingpositive refracting power; wherein the prism component is arranged on anutmost object side among optical elements having refracting power in thezoom optical system; wherein the lens group comprises two or more movingoptical units which are moved when at least either zooming or focusingis carried out; wherein the zoom optical system comprises, in order fromthe object side: a first group comprising the prism component and havingnegative refracting power, a second group comprising an aperture stopand having positive refracting power, a third group having negativerefracting power, and a fourth group having positive refracting power;wherein the second group and the third group are the moving opticalunits; and wherein, when zooming is carried out from a wide angle end toa telephoto end, the second group and the third group are moved towardthe object side respectively, an interval between the first group andthe second group decreases, and an interval between the third group andthe fourth group increases.
 9. An image pickup apparatus comprising azoom optical system and an image pickup element; wherein the zoomoptical system comprises: a first group comprising a prism component,the prism component being arranged on an utmost object side in the zoomoptical system and having an entrance surface with a concave surfacedirected toward the object side, a reflecting surface and an exitsurface, two or more moving optical units arranged on an image side ofthe first group and configured to be movable in zooming, a last grouparranged on an utmost image side in the zoom optical system and havingpositive refracting power, and an aperture stop arranged between thefirst group and the last group; wherein, when zooming is carried outfrom a wide angle end to a telephoto end, an entranced pupil formed ofthe aperture stop is moved toward the object side and an exit pupilformed of the aperture stop by an optical system arranged on the objectside of the last group is moved toward the object side; wherein the lastgroup comprises a lens component having an object-side surface which isa first aspherical surface and an image-side surface which is a secondaspherical surface, the second aspherical surface having a convex facedirected toward the image side near an optical axis and having a pointof inflection on a cross-section take along the optical axis; whereinthe first aspherical surface and the second aspherical surface satisfythe following conditions (3) to (5):0.08<(ha11−ha07)/I<0.3  (3)−011<ha07/I<0.07  (4)0.45<Cb/I<1  (5) where ha07 is a distance, in a direction along theoptical axis, from a reference plane to the first aspherical surface ata height of 35% of an effective diagonal length of the image pickupelement from the optical axis; ha11 is a distance, in the directionalong the optical axis, from the reference plane to the first asphericalsurface at a height of 55% of the effective diagonal length of the imagepickup element from the optical axis; I is 50% of the effective diagonallength of the image pickup element; and Cb is a height from the opticalaxis to the point of inflection of the second aspherical surface, thereference plane being determined as normal to the optical axis andtangent to the first aspherical surface at a vortex thereof and adistance from the reference plane in a direction toward an image sidebeing given a positive value; wherein the zoom optical system comprises,in order from an object side: the first group comprising the prismcomponent, the first group having negative refracting power, a secondgroup comprising the aperture stop and having positive refracting power,a third group having negative refracting power, and a fourth grouphaving positive refracting power; wherein the second group and the thirdgroup are the moving optical units, and when zooming is carried out fromthe wide angle end to the telephoto end, the second group and the thirdgroup are moved toward the object side respectively, an interval betweenthe first group and the second group decreases, and an interval betweenthe third group and the fourth group increases.
 10. An image pickupapparatus comprising a zoom optical system and an image pickup element;wherein the zoom optical system comprises: a prism component arranged onan utmost object side and comprising an entrance surface with a concavesurface directed toward the object side, a reflecting surface and anexit surface, and at least one moving optical unit having refractingpower and adapted to be movable; wherein the following conditions (6) to(8) are satisfied:−4<rp1/I<1.8  (6)8<L/I<12  (7)2.5<M/I<7  (8) where rp1 is a radius of curvature of the entrancesurface of the prism component, L is an optical path length of the zoomoptical system, I is 50% of an effective diagonal length of the imagepickup element, M is a total amount of movement of each moving opticalunit at a wide angle end and at a telephoto end, and a focal length atthe telephoto end is 2.3 times or more and 5 times or less of a focallength at the wide angle end; wherein the zoom optical system comprises,in order from an object side: a first group comprising the prismcomponent and having negative refracting power, a second groupcomprising an aperture stop and having positive refracting power, athird group having negative refracting power, and a fourth group havingpositive refracting power; wherein the second group and the third groupare the moving optical units; and wherein, when zooming is carried outfrom the wide angle end to the telephoto end, the second group and thethird group are moved toward the object side respectively, an intervalbetween the first group and the second group decreases, and an intervalbetween the third group and the fourth group increases.
 11. The zoomoptical system according to one of claims 1, 2, 3 and 8, wherein thethird group comprises one negative lens, and a total number of lens inthe third group is
 1. 12. The image pickup apparatus according to claim9 or 10, wherein the third group comprises one negative lens, and atotal number of lens in the third group is
 1. 13. The zoom opticalsystem according to claim 11, wherein the negative lens constituting thethird group is a plastic lens.
 14. The image pickup apparatus accordingto claim 12, wherein the negative lens constituting the third group is aplastic lens.
 15. The zoom optical system according to one of claims 1,2, 3 and 8, wherein the first group further comprises a negative lensand a positive lens which are arranged on an image side of the prismcomponent.
 16. The image pickup apparatus according to claim 9 or 10,wherein the first group further comprises a negative lens and a positivelens which are arranged on an image side of the prism component.
 17. Thezoom optical system according to claim 15, wherein refractive indexes ofthe negative lens and the positive lens of the first group are 1.7 ormore, respectively.
 18. The image pickup apparatus according to claim16, wherein refractive indexes of the negative lens and the positivelens of the first group are 1.7 or more, respectively.
 19. The zoomoptical system according to claim 15, wherein the negative lens and thepositive lens of the first group are cemented together.
 20. The imagepickup apparatus according to claim 16, wherein the negative lens andthe positive lens of the first group are cemented together.
 21. The zoomoptical system according to one of claims 1, 2, 3 and 8, wherein thesecond group comprises, in order from an object side, a first positivelens, a second positive lens, and a negative lens, and a total number oflenses contained in the second group is
 3. 22. The image pickupapparatus according to claim 9 or 10, wherein the second groupcomprises, in order from an object side, a first positive lens, a secondpositive lens, and a negative lens, and a total number of lensescontained in the second group is
 3. 23. The zoom optical systemaccording to claim 21, wherein the first positive lens of the secondgroup is a double aspherical lens made of plastic, and refractiveindexes of the second positive lens and the negative lens of the secondgroup are 1.7 or more, respectively.
 24. The image pickup apparatusaccording to claim 22, wherein the first positive lens of the secondgroup is a double aspherical lens made of plastic, and refractiveindexes of the second positive lens and the negative lens of the secondgroup are 1.7 or more, respectively.
 25. The zoom optical systemaccording to one of claims 1, 2, 3 and 8, wherein the fourth groupcomprises a positive lens, and a total number of lens in the fourthgroup is
 1. 26. The image pickup apparatus according to claim 9 or 10,wherein the fourth group comprises a positive lens, and a total numberof lens in the fourth group is
 1. 27. The zoom optical system accordingto one of claims 1, 2 and 3, wherein a total number of reflectingsurface included in the prism component is
 1. 28. The zoom opticalsystem according to one of claims 1, 2 and 3, wherein there is nointermediate image forming surface in the prism component.
 29. The zoomoptical system according to one of claims 1, 2 and 3, wherein anincident light axis is deflected by a right angle as being reflected onthe reflecting surface of the prism component.
 30. An image pickupapparatus comprising: the zoom optical system according to one of claims1, 2 and 3; and an image pickup element arranged on an image side of thezoom optical system.